CO.sub.2 (carbon dioxide) laser radiation is widely used to create surgical incisions internally of a human body. While the principal component of CO.sub.2 radiation, i.e., 10.6 microns in wavelength, interacts favorably with tissue for surgery, it is not a straight forward process to deliver the same efficiently to a surgical site. U.S. patent application Ser. No. 07/164,236, filed Mar. 4, 1988, the disclosure of which is hereby incorporated herein by reference and which is owned by the assignee of this application is directed to a method and arrangements found to be particularly useful for delivering such radiation. U.S. patent application Ser. No. 07/181,448, filed Apr. 14, 1988 owned by the same assignee and naming, like the above application, one of the inventors herein, is directed to an end probe which takes advantage of using the conditions discussed below in a hollow waveguide made from a single crystal material.
There is an anomalous dispersion phenomenon that is associated with transmission of 10.6 micron radiation. As pointed out in the paper entitled "Dispersion Phenomena in Hollow Alumina Waveguides" (1985) authored by Jenkins, et al. and appearing at pages 1722, et seq. of the IEEE Journal of Quantum Electronics, Vol. QE-21, it has been discovered that the attenuation of 10.6 micron radiation by a hollow air core alumina waveguide is significantly lower than it is for other longer or shorter wavelengths. This phenomenon has been associated with the index of refraction (n) of the waveguide for 10.6 micron radiation. That is, this unexpected phenomenon has been associated with the index of refraction of the cladding of a hollow air core waveguide being less than one, the index of refraction of air, at such wavelength. A hollow waveguide of the type to which the invention relates is commonly referred to as a "n&lt;1" waveguide.
As mentioned previously, 10.6 micron radiation is used for internal surgery. It is important that a physician implementing such surgery within a body have a view of the surgery which he or she is performing. Generally, such visualization is achieved by locating a viewing telescope or a fiber optic viewing probe at the surgical site. In many of such applications, an endoscope is used both to house a radiation delivery probe and a viewing telescope or fiber optic device. For example, in gynecology, a laparoscope (a specialized endoscope) can be used to house both an n&lt;1 waveguide and a right angle offset viewing telescope. In many medical applications, however, a surgeon often wishes to view a treatment site by the unaided eye in a line-of-sight manner or by using a straight telescope. Specifically, a straight rod-lens telescope is placed in the central lumen of, for example, a bronchoscope. It will be recognized that it is impractical to also use such a bronchoscope to deliver CO.sub.2 radiation to the site in a conventional manner, i.e., by focusing the radiation to a small spot at the distal end of the bronchoscope. Since the free laser beam would occupy the entire central lumen of the endoscope, there is no space for introducing other instruments, such as a viewing telescope, down the endoscope while the laser is in use. Also, the walls of the central lumen of a typical endoscope will not efficiently guide CO.sub.2 radiation. Thus, it is quite advantageous for one to be able to use an n&lt;1 waveguide to convey the CO.sub.2 radiation to the surgical site since such conveyance does not rely on the endoscope except as a protective device. The difficulty, though, is that with n&lt;1 guides and other delivery systems for 10.6 micron radiation that only utilize the endoscope as a protective housing, the construction of the same has resulted in obstruction of straight or line-of-sight viewing through the endoscope, with the result that their use is not as widely applicable as desired. While at first blush it would appear that a right-angle coupler of a standard design could be used to couple 10.6 micron radiation from a delivery system to an n&lt;1 guide, it is recognized by those skilled in the art that the bulky construction of a conventional coupler will provide the same obstruction problems.